Heat exchanger with ribbed fin

ABSTRACT

The invention is, on the one hand, a heat exchanger comprising at least one tube (1) and at least one ribbing made of a heat conducting material folded to a concertina-like shape, where the ribbing has ribs (2), each of them being substantially perpendicular to the axis (10) of the tube (1) and comprising wings (4A, 4B) and a rib base (3) between them, and where the ribs (2) are attached to the tube (1) at their rib base (3). At least one of said wings (4A, 4B) of each ribs (2) comprises patterns interrupting the continuity of the wing material, and/or bent surfaces making an acute angle (α) to a plane perpendicular to the axis (10) of the tube (1). The patterns may be cutouts (7A, 7B), holes (8), outpressed parts (9) or embossings (17A, 17B). The invention is, on the other hand, a method of making a heat exchanger comprising forming ribs (2 ) by folding a strip of a heat conducting material to a concertina-like shape and attaching the ribs (2) of the folded material to a tube (1) transversally, where before the folding cutouts (7A, 7B), holes (8) and/or outpressed parts (9) are formed on parts of the strip corresponding to the ribs (2), and/or after having attached the ribs (2) to the tube (1) at least a part of the surface of the ribs (2) is bent as compared to a plane perpendicular to the axis (10) of said tube (1).

This is a continuation of co-pending application Ser. No. 438,858 filedon Oct. 21, 1982, now abandoned.

FIELD OF THE INVENTION

The subject matter of the invention is a heat exchanger comprising atleast one tube and at least one ribbing made of a heat conductingmaterial folded to a concertina-like shape, where the ribbing folds haveribs, each of them being substantially perpendicular to the axis of thetube and comprising wings and a rib base between them, and where theribs are attached to the tube at their rib base.

BACKGROUND OF THE INVENTION

There is a known heat exchanger comprising a tube and a wire ribbingattached to it, in which the wire after expedient deformation is foldedto a concertina-like shape, and then attached to the mantle of the tubealong one of its generatrices by a permanent joint, e.g. welding orsoldering. Such a heat exchanger is described in the Hungarian Pat. No.153,573.

A lamellar cooling ribbing is known furthermore from the Hungarian Pat.No. 144,706, where a metal strip folded in a zigzag shape is insertedbetween two cooling tubes, and where the metal strip constitutes thecooling ribbing.

In both of the above mentioned devices the ribs are of a continuousmaterial and their surfaces stand in the direction of flow of the mediumstreaming at a right angle to the tube axis. Heat exchangers of thistype have the advantage that their production can easily be automated,and that they can be produced in a welded construction as well, i.e.they can be used even in cases of high temperature.

OBJECT OF THE INVENTION

The object of the present invention is to provide a novel heat exchangerof the aforedescribed type with improved heat engineeringcharacteristics without making its production essentially morecomplicated or expensive.

SUMMARY OF THE INVENTION

The invention is based on the discovery that patterns interrupting thecontinuity of the material (e.g. discontinuities such as cutouts,outpressed parts or embossings) applied on parts of the folded heatconducting material (e.g. metal strip) constituting the ribs and/orbends result in an essential improvement of the heat-transfercharacteristics of the heat exchanger. In order to make these patternsor bendings only an insignificant enlargement or modification of theproduction line producing ribbed heat exchangers is needed.

Thus the invention is a heat exchanger comprising at least one tube andat least one ribbing made of a heat conducting material folded to aconcertina-like shape, where said ribbing has ribs each of them beingsubstantially perpendicular to the axis of said tube and comprisingwings and a rib base between them and where said ribs are attached tosaid tube at their rib base. According to the invention at least one ofsaid wings of each ribs comprises patterns interrupting the continuityof the wing material and/or bent surfaces making an acute angle to aplane perpendicular to the axis of said tube. The heat conductingmaterial folded to a concertina-like shape is preferably a metal strip,but can also be e.g. a deformed wire on which sections of across-section corresponding to ribs are formed.

In an advantageous embodiment of the heat exchanger according to theinvention each of said ribs has at the end of its wings connectingparts, each of them joined to an adjacent rib and at least one of saidconnecting parts is twisted at an acute angle as compared to the ribbase. According to a further embodiment, both connecting parts aretwisted at an acute angle of same magnitude but of opposite directionwith respect to the rib base.

According to another embodiment, the ribs are bent at their rib basesattached to said tube at an acute angle with respect to a planeperpendicular to the tube axis. This embodiment results in a one-waybending of the whole ribbing.

The bending of the ribs is facilitated in an embodiment, where each ofsaid ribs has at the end of its wings connecting parts, each of themjoined to an adjacent rib and provided with a first cutout, and the partof each rib above the first cutouts is bent at an acute angle ascompared to a plane perpendicular to the axis of the tube. Preferablyeach of the ribs is provided with a second cutout on a side of its ribbase, the side being opposite to the tube, and the parts of the wingsabove said first cutouts being bent at an opposite direction as comparedto a plane perpendicular to the axis of said tube.

According to a further advantageous embodiment, said patterns are formedby embossings made on said wings.

In another embodiment of the heat exchanger each of said ribs has at theend of its wings connecting parts, each of them joined to an adjacentrib, and said patterns are formed by third cutouts beginning in saidconnecting parts and extending towards the rib base lengthwise alongsaid wings.

According to a further embodiment, the patterns are formed by holesand/or outpressed parts improving the heat exchange by interrupting thewing material.

In an advantageous embodiment of the heat exchanger, said ribs arewelded through outfolds formed at the rib base to said tube having around cross-section, and said outfolds have a form fitting to the tubein a peripheral range of at least 60°. Such a joining ensures good heattransfer and resistance.

In another highly advantageous embodiment of the heat exchangeraccording to the invention, two ribbings made of a folded material areattached to the tube on opposite sides thereof, and the two ribbingshave ribs comprising wings with a surface bent in an opposite directionas compared to each other. Expediently, openings are formed on theopposingly bent wings of the ribbings.

The invention further relates to a method of making a heat exchangerwith ribs. One method according to the invention comprises the steps offorming ribs by folding a strip of a heat conducting material to aconcertina-like shape and attaching the ribs of the folded material to atube transversally, where before the folding cutouts, holes and/oroutpressed parts are formed on parts of the strip corresponding to theribs; and/or after having attached the ribs to the tube at least a partof the surface of the ribs is bent as compared to a plane perpendicularto the axis of the tube.

Another method according to the invention comprises the steps of formingsections of a cross-section corresponding to ribs by continuous orintermittent deformation of a wire of a heat conducting material,folding the deformed wire to a concertina-like shape and, having beenfolded, attaching the sections to a tube transversally, where before thefolding cutouts, holes and/or outpressed parts are formed on saidsections of a cross-section corresponding to ribs; and/or after havingattached the sections of a cross-section corresponding to ribs to thetube, at least a part of the surface of the sections is bent as comparedto a plane perpendicular to the axis of said tube.

The above mentioned two procedures, forming of cutouts, holes and/oroutpressed parts on the one hand and bending on the other, can beapplied jointly as well.

In an advantageous embodiment of the method said attaching is performedby welding.

In a further expedient embodiment of the method according to theinvention, before the folding semi-circular outfolds are formed on theedge of the middle part of said ribs or sections, said ribs or sectionsare attached to the tube by spot-welding said outfolds.

Cutouts, outpressed parts or embossings can continuously be made on theribbing of the heat exchanger according to the invention, e.g. beforefolding and welding it to the tube, with a simple press die by atechnology known per se. These then will not disturb the furtherprocedures such as folding to a concertina-like shape and welding. In acase when bending procedures are carried out after having welded saidribbing to the tube, the welding head can easily enter among the stillunbent straight ribs, and this makes closed-spaced ribbing possible,which is advantageous from the point of view of heat engineering.

By the help of the solution according to the invention, the veryeffective continuous method of making ribbed tubes--what is one of themost economical methods of producing heat exchangers with weldedtransversal ribbing--can be made suitable for the production of heatexchangers of which it is sufficient to build in 30 to 50% less than ofknown types for solving the same heat.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be hereinafter described on basis of advantageousembodiments as shown in the drawing, wherein:

FIG. 1 is a perspective detail view of an embodiment of the heatexchanger according to the invention,

FIGS. 2 and 3 are sectional views of two further embodiments,

FIG. 4 is a sectional view taken along the line A--A in FIG. 3,

FIG. 5 is a sectional view of a further embodiment,

FIGS. 6 and 7 are perspective detail views of two further embodiments,

FIG. 8 is a sectional view of a further embodiment,

FIG. 9 is a sectional view taken along the line B--B in FIG. 8,

FIGS. 10, 11 and 12 are perspective detail views of three furtherembodiments,

FIG. 13 is a sectional view of a further embodiment taken along the lineD--D in FIG. 14,

FIG. 14 is a sectional view taken along the line C--C in FIG. 13, and

FIG. 15 is a top view of a detail of the embodiment according to FIGS.13 and 14.

SPECIFIC DESCRIPTION

Identical elements--or those with an identical function--are indicatedby identical reference signs in the figures. In FIG. 1 two ribbingsfolded to a concertina-like shape are attached to a tube 1, from theribs of which only ribs 12, 2, 22 and 12', 2', 22' can be seen in thedrawing. The ribs of both ribbings are placed along the axis 10 of thetube 1 nearly parallel and in front of each other. The rib 2 has twowings 4A and 4B and a rib base 3 between them. The rib 2 is joined tothe two adjacent ribs 12 and 22 with connecting parts 5A and 5B at theend of said wings 4A and 4B. Similarly, rib 2' is joined to adjacentribs 12' and 22' with connecting parts 5A' and 5B'. The ribs 2 and 2'are welded to the tube 1 at the rib base 3 and 3' respectively. Ribs 2and 2' are substantially perpendicular to the axis 10 of the tube 1. Thedirection of flow of the medium, shown by arrows 21, is nearly parallelwith the plane of ribs 2 and 2'. According to the invention, cutouts 7Aand 7B are formed in the connecting parts 5A and 5B, extending along thewings 4A and 4B towards the rib base 3 parallel with the edges of thewings 4A and 4B, then slightly descending in order to ensure favourableheat conducting conditions in the rib 2. The rib 2' has similar cutouts7A' and 7B', but here the cutouts 7A' and 7B' go ascending when gettingnearer to the tube 1. The dimension of the rib 2 in the direction of theflow would be L_(o) without cutouts 7A and 7B. When taking said cutouts7A and 7B into consideration, this dimension is L, which is smaller thanthe half of the dimension L_(o). According to our measurings, cutouts 7Aand 7B applied in case of a flow velocity of 2 to 10 m/sec and adimension L_(o) of 1 to 3 centimeters result in an 30 to 50% improvementof the heat transfer.

In FIG. 2 a line of holes 8 is formed in the middle of the rib 2.Connecting parts 5A and 5B are perforated by cutouts in order to ensurea better flexibility. The rib 2' is formed in a similar way. Here theboundary layer formed on the rib wings 4A and 4B is interrupted by theholes 8.

In this embodiment the heat transfer will not improve to such an extentas in the embodiment according to FIG. 1, nevertheless it can be ratheradvantageous in many cases because of the simplicity of the perforatingprocedure and because the smaller pressure drop occuring on the ribs.

In FIG. 3 the rib 2 is provided with outpressed parts 9, as it can beseen in FIG. 4, which "redirect" the flow medium according to arrows 21through the openings formed at said outpressed parts 9. Here theoutpressed parts 9 function also as a heat transmitting surface. Thissolution is, from the point of view of heat engineering, highlyadvantageous, and can be applied mainly in cases where the flow mediumdoes not tend to form a deposit.

According to the embodiment shown in FIG. 5, three outpressed parts 9are formed around the rib base 3 beside cutouts 11A and 11B applied onconnecting parts 5A and 5B and extending along wings 4A and 4B inwards.These outpressed parts 9 can be the same as those shown in FIG. 4. Inthis case the heat transfer of the wings 4A and 4B is improved by saidcutouts 11A and 11B, while that of the surfaces near the tube 1 isimproved by said outpressed parts 9. The latters ensure at the same timethe flushing of dead areas formed behind the tube 1, making thereby theformation of a slack medium area impossible.

FIG. 6 illustrates an embodiment provided with bent ribs 12, 2 and 22.The unbent position of the rib 2 is shown by a dotted line. A generatrix13 at the rib base 3 and an other generatrix 15 at the connecting part5B of the rib 2 are perpendicular to the axis 10 of the tube 1. Thegeneratrix 14A of the connecting part 5A is twisted at an acute angle αas compared to the vertical generatrix 14. Thus the wing 4A has asurface twisted and bent at the same time. The ribs 12 and 22 behind andbefore said rib 2, respectively, as well as the other ribs not shown inthe drawing are, of course, bent in a similar way.

The embodiment shown in FIG. 6 can be realized in a form, too where thewing 4B is also twisted at the connecting part 5B, in an expedient case,at an acute angle α as compared to the vertical generatrix 15 in adirection opposite to that of the generatrix 14A. Nevertheless there maybe another embodiment where the angles of twisting are not identical orwhere the direction of twisting is the same at both wings 4A and 4B. Bythe help of these different bendings the heat exchanger can be appliedto special conditions of given places achieving thus e.g. the turningaway of the medium stream.

It is especially advantageous if the angles of twisting mentioned in theprevious paragraph are of an opposite direction, i.e. the two wings 4Aand 4B of one and the same rib 2 are twisted in opposite directions and,at the same time, the direction of twisting of the wings belonging tothe rib 2' (not shown in FIG. 6) attached to the other side of the tube1 is opposite to the direction of twisting of the wings 4A and 4B. Inthis case the wings of the ribs attached to the tube 1 on the side ofthe incoming flow medium will direct the flow medium into twodirections, while the wings of the ribs attached to the tube 1 on theother side will return the flow medium again. This embodiment hasspecial advantages with regard to its installation because of thesymmetry of the heat exchanger.

From the point of view of manufacturing technology, it is advantageousif the whole rib 2 is bent in a single step by bending its part at therib base 3 welded to the tube 1. Such an embodiment is shown in FIG. 7,where generatrix 13A of the middle part of said rib 2 near to the ribbase 3 is bent at an acute angle α as compared to generatrix 13perpendicular to the axis 10 of the tube 1, so that the whole rib 2 isbent in a nearly acute angle α as compared to a plane perpendicular tothe axis 10.

From the point of view of hydrodynamics, it is advantageous to formpatterns on the surface of the wings 4A and 4B of the rib 2, preferablybefore the folding, by making embossings 17A and 17B as shown in FIGS. 8and 9.

FIG. 10 shows an embodiment in which the connecting parts 5A and 5Bbetween the rib 2 and the adjacent ribs (of which only the rib 12 can beseen in the drawing) are provided with half-side cutouts 18A and 18B,where said cutouts 18A and 18B make, at the same time, the folding to aconcertina-like shape easier. In this case the bending of the upper partof the rib 2 can be carried out even after having welded the stripfolded to a concertina-like shape to the tube 1. The position of theribs 2 and 12 before their bending is shown by a dotted line; andgeneratrices 14A and 15A of the bent wings 4A and 4B make an acute angleα to generatrices 14 and 15 previous to the bending, respectively.

FIG. 11 shows an embodiment where the cutouts 19A and 19B in theconnecting parts 5A and 5B can be found only in the middle forincreasing the mechanical strength of the ribbing. In case of such anembodiment, the part of the rib 2 above cutouts 19A and 19B can easilybe bent at an acute angle α as compared to a plane perpendicular to theaxis 10 of the tube 1. FIG. 11 shows the rib 2 in an unbent position;its bent position is marked by generatrix 13A which stands in an acuteangle α as compared to generatrix 13 of the still unbent rib 2.

It may be advantageous if the embodiment shown in FIG. 10 is modified ina way that the wings 4A and 4B are bent at an opposite direction ascompared to each other. Such an embodiment is shown in FIG. 12, here afurther cutout 20 is formed in the middle part between the wings 4A and4B, at the rib base 3, what makes the bending of the upper parts of saidwings 4A and 4B in an opposite direction easier; this bendingproceeds--according to the embodiment shown here--at an identical acuteangle α. The position previous to bending is shown by a dotted line inthis figure, too.

From the point of view of heat engineering and manufacturing technology,a special advantage can be achieved if cutouts, holes, outpressed partsand bendings are applied jointly as in the embodiment shown in FIGS. 13to 15. FIG. 13 is a sectional view taken along the line D--D in FIG. 14,FIG. 14 is a sectional view taken along the line C--C in FIG. 13, andFIG. 15 is a top plan view where the ribbing attached to the lower partof the tube 1 is not shown for the sake of better visibility. In case ofthis embodiment the cutouts 19A and 19B applied at the connecting parts5A and 5B of the rib 2, as well as the openings 24A and 24B in the wings4A and 4B make the bending of the upper part of the rib 2 especiallyeasy in case of a ribbing having been welded to the tube 1 previously.Further a hole 25 is formed in the middle part of the rib 2. Similarly,the rib 2' of the ribbing attached to the other side of the tube 1 isprovided with cutouts 19A' and 19B' as well with a hole 25'. As aconsequence of the bending, a pressure difference appears between thetwo sides of the ribs (e.g. those of the rib 2) for fluid mechanicalreasons. Because of this, a flow will start through the openings 24A and24B as well as through the hole 25 placed in the bending, what draws theboundary layer 27, thus improving heat transfer in a significant degree.It can be seen in FIG. 13 that the ribbings on the two opposite sides ofthe tube 1 are bent in a direction opposite to each other. The ribs 12,2 and 22 are bent to the right at an acute angle α as compared with aplane perpendicular to the axis 10, while the ribs 12', 2' and 22' arebent to the left also at an acute angle α, preferably at an angle of 20°to 25°. The ribs 12, 2 and 22 are provided with outfolds 16, 6 and 26,respectively, which fit to the tube 1 at a peripheral range of at least60°. The ribs 12, 2 and 22 of the one ribbing can be attached to thetube 1 at the outfolds 16, 6 and 26 by point-welding. Similarly, theribs 12', 2' and 22' of the other ribbing on the opposite side of thetube 1 are point-welded to said tube 1 at the outfolds 16', 6' and 26'.

In the shown embodiments of the heat exchanger according to theinvention, the ribs are substantially parallel with each other, andtheir longitudinal axis is substantially perpendicular to the axis 10 ofthe tube 1. This is not necessarily so, there may be other embodimentswhere the ribbing is formed in a zigzag shape, i.e. the adjacent ribsare not parallel with each other, but there is an acute angle betweenthem. According to a further embodiment all the ribs are parallel witheach other but their longitudinal axis makes an angle to the axis 10 ofthe tube 1 different from 90°. From the point of view of the invention,the only essential fact is that the ribbing should be in relation to thetube a transversal ribbing. The tube can also have an othercross-section than that of a circular ring.

There can be several tubes arranged in a suitable way as compared toeach other in the heat exchanger according to the invention. Each ofthese should be provided with a ribbing formed according to theinvention. The ribbing may be only on one side of the tube or on bothsides facing each other. The ribbing and the tube can be attached toeach other by welding, soldering or by any other procedure known per se.

In case of the embodiments shown in the drawings, the heat conductingmaterial folded to a concertina-like shape is a metal strip. However,this is--according to the invention--not an absolute necessity. Theessential point is that the material folded to a concertina-like shapeshould have parts constituting wings having a cross-section of anelongated plane figure, e.g. in case of a strip a rectangle, thelongitudinal axis of which is substantially perpendicular to the axis ofthe tube, leaving the possible bending of the wing according to theinvention out of consideration. The elongated plane figure can, however,have outlines different from straight lines, e.g. two circular arcs. Inthis case the cross-section of the wings is shaped which is advantageousfrom a hydrodynamic point of view.

When producing a heat exchanger according to the invention, one canstart with a heat conducting strip or wire material. It can beadvantageous e.g. to apply a metal strip. In case when some wire of agiven cross-section is taken as the starting material, e.g. aluminiumwire of a round cross-section, the sections of a nearly rectangularcross-section corresponding to wings can be produced first by colddeformation. It is not an absolute necessity that the wire parts betweenthese sections should also have a nearly rectangular cross-section.According to the invention cutouts, holes, embossings and/or outpressedparts are formed before the folding, while the bending of the ribsfollows the attachment, preferably welding of the ribbing to the tube.

What is claimed is:
 1. In a heat exchanger, a heat-exchanger elementwhich comprises:a tube composed of a heat-conducting material; and tworibbing strips secured to said tube in said heat-conducting relationshiptherewith, said strips being disposed on diametrically opposite sides ofsaid tube, each of said strips comprising:respective transverse portionsextending across the tube and having a central portion formed with anarcuate recess receiving the tube and a pair of wings projectinglaterally outwardly beyond said tube and cantilevered therefrom, each ofsaid wings being connected to a wing of an adjacent transverse portionby connecting portions, the transverse portions having widthssubstantially smaller than their lengths, each of said central portionsbeing formed with a plurality of arcuate cutouts from which portions arebent to intercept a flowing fluid, each of said wings being formed withelongated cutouts extending into the respective connecting portions andterminating at said central portions, and said strips being separatedfrom one another across said tube by a gap approximately equal to theinternal diameter of said tube.
 2. A heat exchanger comprising:at leastone tube made of a heat conducting material for circulating a firstfluid medium, for each tube two strip ribbings attached to said tube inheat-conducting relationship along diametrically opposite sides of saidtube to increase the heat exchange between the first fluid medium and asecond fluid medium passing the tube substantially parallel to surfacesof said ribbings, each of said ribbings being made of a heat conductingstrip material folded to an accordion-like shape to form a plurality ofspaced ribs and connecting parts connecting the adjacent ribs atalternate ends, each of said ribs comprising two wings overhangingopposite sides of said tube and a rib base between said wings, saidoverhanging wings of each rib being separated by a gap from theoverhanging wings of the other ribbing of the respective tube, saidconnecting parts being joined with the ends of the wings of the adjacentribs, each of said ribbings being attached to said tube at its rib basesalong one side of said tube so that the ribs extend transversely to anaxis of said tube and the two ribbings are not in direct contact witheach other, each of said ribs comprising at least one discontinuityinterrupting the continuity of the wing material in the direction oflines along which the ribbing is folded whereby boundary layers of thesecond fluid medium formed along the wing surfaces are at least partlyinterrupted, said discontinuity comprising a cutout beginning in theconnecting part and extending lengthwise along the wing.
 3. The heatexchanger according to claim 2 wherein said ribs comprise furtherdiscontinuities in the form of openings made in said wings.
 4. The heatexchanger according to claim 2 wherein said ribs comprise furtherdiscontinuities in the form of outpressed parts made in said wings. 5.The heat exchanger according to claim 2 wherein said ribs are weldedthrough outfolds formed at the rib base to said tube having a roundcross-section, and said outfolds have a form fitting to said tube in aperipheral range of at least 60°.
 6. The heat exchanger according toclaim 2 wherein each of said ribs comprises at least one wing havingbent surfaces making an acute angle with respect to a planeperpendicular to the axis of said tube.
 7. The heat exchanger accordingto claim 6 wherein said connecting parts are narrower than said ribs inthe direction of said folding lines and the part of each rib extendingover the respective connecting parts is bent at an acute angle withrespect to a plane perpendicular to the axis of said tube.
 8. The heatexchanger according to claim 6 wherein the ribs of said two ribbingsattached to each tube have surfaces bent at an acute angle in oppositedirections with respect to a plane perpendicular to the axis of saidtube.
 9. The heat exchanger according to claim 8 wherein said ribscomprise further discontinuities in the form of openings.